Many typical wireless communications networks include multiple transmitters and multiple receivers desiring to communicate at the same time over the same frequencies (e.g., according to communications standards, such as CDMA 2000, UMTS, LTE, 802.11, etc.). For example, a typical cellular environment can have many base stations communicating with many cellular devices (e.g., phones); and a typical WiFi environment can have multiple WiFi access points communicating with multiple users (e.g., laptops, smart phones, etc.). In such communications networks, there are multiple communications links between transmitters and receivers, and each of those links can potentially interfere with others of those links. Interference and noise in such environments can limit the effective capacity of the communications network. For example, receivers can experience packet loss and bit errors, etc.; and transmitters can be forced to re-send data, send data using more robust schemes (which may use more bandwidth and lower the effective capacity), etc.
To exacerbate these issues, as mobile data communications have dramatically increased, a number of proposed approaches have suggested reducing cell sizes and increasing base station/access point density. Typically, the path loss versus distance curve is flatter at shorter distances and steeper at relatively long distances. As a result, the inter-cell interference can become significant as the cell size/coverage area shrinks. Therefore, joint transmit signal design for interference networks is a key technology for the next generation wireless communication systems. In particular, it can be desirable to maximize the capacity of the network (e.g., the transmission rate) by coordinating and minimizing the interference experienced by the communication links.